68K register management

[Thorham]

I always save all modified registers in the subroutines, unless something needs serious optimizing (most code doesn't).

[ovale]

A bit off topic Is it possible to instruct a C/C++ compiler to never use a set of registers? For example because I want to use them in an interrupt handler without saving registers.

[Rst7]

Originally Posted by ovale

Is it possible to instruct a C/C++ compiler to never use a set of registers? For example because I want to use them in an interrupt handler without saving registers.

Try to use

register volatile long SAVE __asm("d2");

as global variable.

[Antiriad_UK]

I use the OS convention for "slow" code like prototyping functions, and non time critical, where d0-d1/a0-a1 are assumed to be trashed on any call and everything else is saved/restored:

http://amigadev.elowar.com/read/ADCD.../node000F.html

Then for all other code that needs to be fast (demo stuff) I 99% of the time leave $dff000 in a6 and just document everything on subroutine definition and subroutine call. Yes, a bit of a pain when you change a function but there you go. If not documented assumption is that everything is trashed. Within a subroutine I use scratch registers in order from d0 first up to d7 so that when you start nesting function calls in loops the outer loop counters end up being higher up.

	;Load current palette into CL if needed
	bsr	Copper_Write_Palette	;I:a5, T:d0/a0-a2
..
..
..
..

*****************************************************************************
* Loads the current colors into the current copperlist if changed.
* IN:		a5, Controller_Info
* OUT:
* TRASHED:	d0/a0-a2
*****************************************************************************

Copper_Write_Palette: